Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of the common general knowledge in the field.
Wood is a staple construction formulation used throughout the world. However, it is prone to degradation from elements including the natural environment, weather events, insects, rot and fire. Accordingly, a range of chemical treatments has been developed to improve the durability and working lifetime of wooden structures.
To treat and prevent infestations, timber is often impregnated with a preservative such as a fungicide or insecticide. The preservative is typically present in a carrier, with the mixture being applied to the surface of the timber, for example by dipping, spraying, brushing or pressure treatment, such that the carrier and preservative are absorbed in to the timber. As such, the treatment of timber with preservative compounds involves the introduction of stable chemicals into the cellular structure of the timber. This, in turn, protects the timber from hazards such as fungi, insects and other wood-destroying organisms. Preservative treatments may also include the introduction of chemicals that improve resistance to degradation by fire.
In Australia, the treatment of timber is governed by the Australian standard “AS 1604-2012”. Hazard Class H3 is defined as being for protection against “moderate fungal decay and termite hazard” with examples of end uses being decking, fascia, cladding, window reveals, and exterior structure timber. The timber is exposed to the weather or not fully protected. It is clear from the ground and the area is well drained and ventilated. H3 treatment is designed to prevent attack by insects, including termites, and decay.
Hazard Class H4 defines the requirements for “severe decay, borers and termites”, fence posts, greenhouses, pergolas (in ground and landscaping timbers)”. The timber to which H4 is applicable is in contact with the ground or is continually damp so there is a severe decay hazard. The treatment stops attack by insects, including termites, and severe decay.
“Penetration” is defined under the H3/H4 Standards as: “All preservative-treated wood shall show evidence of distribution of the preservative in the penetration zone in accordance with the following requirements: (a) If the species of timber used is of natural durability class 1 or 2, the preservative shall penetrate all the sapwood. Preservative penetration of the heartwood is not required; (b) If the species of timber used is of natural durability class 3 or 4, the preservative shall penetrate all of the sapwood and, in addition one of the following requirements shall apply; (b(i)) Where the lesser cross-sectional dimension is greater than 35 mm, the penetration shall be not less than 8 mm from any surface. Where the lesser cross-sectional dimension is equal or less than 35 mm, the penetration shall be not less than 5 mm from any surface; and (b(ii)) Unpenetrated heartwood shall be permitted, provided that it comprises less than 20% of the cross-section of the piece and does not extend more than halfway through the piece from one surface to the opposite surface and does not exceed half the dimension of the side in the cross-section on which it occurs”.
As mentioned above, a carrier must be used in order to facilitate penetration of the preservative into the timber. As shown in the Australian Standards, the carriers presently available can be characterised broadly as “water-borne” or “solvent-borne” systems.
A carrier must be capable of providing sufficient penetration of the preservative into the wood, thereby to provide an effective barrier against infestation. Other considerations in the choice of carrier include the desired rate of penetration, cost, environmental, health and safety considerations. A carrier may provide for a “complete penetration” formulation, or for an “envelope penetration” formulation in which a defined depth of penetration of one or more preservatives into the wood is achieved.
The preservatives commonly used in timber treatment can be characterised according to the carrier vehicle used to carry preservatives into the timber, and by the active ingredients protecting against the various hazards. Light organic solvent-borne preservatives (LOSPs) comprise a light organic solvent, typically white spirits, to carry the preservative into the timber. The solvent is drawn out in the final stages of treatment, with the preservative remaining within the wood. Such preservatives are typically fungicides, having copper, tin, zinc, azoles and pentachlorophenols (PCPs) as major toxicants. Insecticides such synthetic pyrethroids (e.g., permethrin, cypermthrin or bifenthrin) may be incorporated within the preservative composition if an insect hazard is also present.
One principal advantage of LOSP and other hydrocarbon solvent-based treatments is that the treated timber does not swell, making such treatment suitable for “finished” items such as mouldings and joinery. The majority of LOSPs used in wood treatment also contain mixtures of resin/waxes so as to give the surface water repellent properties. However, odour and exposure to VOCs (volatile organic compounds) can present some environmental/occupational health and safety issues. The LOSP procedure does engender one significant advantage in that it does not add moisture back into the timber. Excessive moisture uptake can affect the dimensional stability of timber.
It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.
The present invention thereby seeks to provide a wood treatment formulation that meets the industry-specific standards of active ingredient retention and penetration. The treated wood should preferably not require re-drying after treatment and have good dimensional stability. The advantages in obtaining an industrially-effective “low odour preservative” formulation may be both economic and environmental.
Low aromatic or dearomatised solvents are proposed herein as an alternative to LOSP/mineral spirits, kerosene, diesel—or indeed any other solvent-based hydrocarbon carrier currently used throughout the wood preservation industry. For example, carriers according to the invention can comprise low odour solvents or mixtures of solvents, which can be considered as dearomatised solvents or low aromatic solvents, that contain wood preservatives for the treatment of wood and wood products.
Low odour solvents have been prescribed in, for instance, International patent publication WO 2000/066668. This document describes a composition comprising: (a) a hydrocarbon component; and (b) an ester component; wherein the composition has: (i) less than 13% vol. of aromatic compounds relative to the total volume of the composition; (ii) a distillation range situated within the range 135-260° C.; and (iii) a Kauri butanol value of 34 or more.
For clarity, it will be appreciated by those of skill in the art that the low odour solvent or solvent mixture need not be free or even substantially free of aromatics; an upper aromatics content of approximately 15% v/v is envisaged. As such—and for the avoidance of doubt, a solvent mixture comprising 85% v/v Exxsol® D40 (discussed below) and 15% v/v kerosene is considered “low odour” for the purposes of the present invention. “Low odour” and “low aromatic” are used synonymously throughout.
A non-limiting example of low aromatic solvents available in industry are those manufactured by ExxonMobil Chemical Company; the Exxsol® D and Isopar® fluid ranges. Such products are purported to give rise to improved health benefits for the workplace by way of a low order of acute toxicity; not classified for skin irritation and does not cause skin sensitisation; lower aromatic leading to increased worker comfort; and non-carcinogenic properties. These solvents also give rise to improved environmental performance such that they do not cause stratospheric ozone depletion. Moreover, Exxsol® D and Isopar® fluids meet certain US FDA Regulations (21 CFR), on an ex-plant basis.
TABLE 1Comparison of health factors using traditional LOSP carriers versus selectedExxsol ® D and Isopar ® fluidsMineralExxsol ®Exxsol ®Isopar ®Isopar ®Isopar ®PropertiesSpiritKeroseneDieselD40D80GLMBoiling150-200° C.150-290° C., 180-365° C., 150-196° C.200-250° C.153-180° C.182-205° C.218-257° C.RangeororwiderwiderFlash Point 35-40° C.37-65° C.>55° C.40° C. min75° C. min40° C. min62° C. min80.5° C. minComposition:Aliphatics✓✓✓✓✓✓✓✓Aromatics✓✓✓     (up to(up to 20 +(up to(<1(<1(<0.05(<0.05(<0.0520 +wt %)30 +wt %)wt %)wt %)wt %)wt %)wt %)wt %)PNAc  ✓     OELa300200 10012001200120012001200mg/m3mg/m3mg/m3mg/m3mg/m3mg/m3mg/m3mg/m3(~50(~40 (~20(197(165(196(171(152ppm)ppm)ppm)ppm)ppm)ppm)ppm)ppm)VHRb~45~100~150131.41240.6“Low”   ✓✓✓✓✓OdouraOccupational exposure limitbVapour hazard ratiocPolynuclear aromatic hydrocarbons
Exxsol® D and Isopar® fluids are well defined solvents, with narrow boiling ranges that have been subjected to additional distillation and refining (cf. kerosene, etc.). When purified to this extent, they are found to be practically free of aromatics, which in turn brings forth perceptible advantages in that traditional aromatic hydrocarbons are associated with adverse health effects.
As can be seen from Table 1, above, mineral spirits, kerosene and diesel have wide boiling ranges; their composition varies significantly; and certain solvent behaviours can on occasion be difficult to predict. They may contain hazardous constituents such as naphthalene and/or ethyl benzene (naphthalene is classified as “Group 28” carcinogen, i.e., possibly carcinogenic to Humans, by the International Agency for Research on Cancer, for effects seen at the nasal area of rodents; ethyl benzene carries the same classification given tumour growth in the kidneys of rodents).
TABLE 2Comparison of potential environmental classification using traditional LOSPcarriers versus selected Exxsol ® D and Isopar ® fluidsMineralExxsol ®Exxsol ®Isopar ®Isopar ®PropertiesSpiritKeroseneDieselD40D80GLCurrent EUR51/53R51/53R51/53NotNotR53NotclassificationclassifiedclassifiedclassifiedPredictedAcute IIAcute IIAcute IIChronicChronicAcuteNotGHSChronic IIChronic IIChronic IIIVIVIIIclassifiedclassificationChronicIII51/53: Toxic to aquatic organisms, may cause long term adverse effects in the aquatic environmentR53: May cause long term adverse effects in the aquatic environmentGHS: Globally harmonised system of classification and labelling of chemicals
Diesel, on the other hand, contains polynuclear aromatic hydrocarbons (PNAs). Certain PNAs have carcinogenic properties—and indeed, diesel is classified for carcinogenicity in Europe.
By comparison, Exxsol® D and Isopar® fluids have a significantly higher Occupational Exposure Limit. Exxsol® D and Isopar® fluids are free of naphthalene and ethyl benzene. Further, the Vapour Hazard Ratio (VHR) for Exxsol® D & Isopar® fluids are significantly lower than the corresponding measures for mineral spirits, kerosene or diesel, meaning that it is far easier to be “overexposed” to traditional wood preservative carriers. In fact, low aromatic solvents can be so gentle as to allow for their use within personal care products. To this end, the Isopar® fluids are registered with the Personal Care Products Council (formerly, the CTFA).
Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise”, “comprising”, and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”.
Although the invention will be described with reference to specific examples it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.